Flexcan Control Register (Canctrl) - Freescale Semiconductor MCF52277 Reference Manual

23.3.2

FlexCAN Control Register (CANCTRL)

CANCTRL is defined for specific FlexCAN control features related to the CAN bus, such as bit-rate,
programmable sampling point within an Rx bit, loop back mode, listen-only mode, bus off recovery
behavior, and interrupt enabling. It also determines the division factor for the clock prescaler. Most of the
fields in this register should only be changed while the module is disabled or in freeze mode. Exceptions
are the BOFFMSK, ERRMSK, and BOFFREC bits, which can be accessed at any time.
Address: 0xFC02_0004 (CANCTRL)
31 30 29
R
W
Reset 0 0
15 14 13
R BOFF
ERR CLK_
MSK MSK SRC
W
Reset 0 0
Field
31–24 Prescaler division factor. Defines the ratio between the clock source frequency (set by CLK_SRC bit) and the serial
PRESDIV clock (S clock) frequency. The S clock period defines the time quantum of the CAN protocol. For the reset value,
the S clock frequency is equal to the clock source frequency. The maximum value of this register is 0xFF, that gives
a minimum S clock frequency equal to the clock source frequency divided by 256. For more information refer to
Section 23.3.19, "Bit
23–22 Resynchronization jump width. Defines the maximum number of time quanta (one time quantum is equal to the S
RJW clock period) that a bit time can be changed by one resynchronization. The valid programmable values are 0–3.
21–19 Phase buffer segment 1. Defines the length of phase buffer segment 1 in the bit time. The valid programmable
PSEG1 values are 0–7.
18–16 Phase buffer segment 2. Defines the length of phase buffer segment 2 in the bit time. The valid programmable
PSEG2 values are 1–7.
15 Bus off interrupt mask.
BOFFMSK 0 Bus off interrupt disabled
1 Bus off interrupt enabled
Freescale Semiconductor
28 27 26
PRESDIV
0 0 0 0
12 11 10
0 0
LPB
0 0 0 0
Figure 23-6. FlexCAN Control Register (CANCTRL)
Table 23-3. CANCTRL Field Descriptions
Timing."
S clock frequency
Resync jump width = (RJW + 1) time quanta
Phase buffer segment 1
Phase buffer segment 2
MCF52277 Reference Manual, Rev. 1
25 24 23 22
RJW
0 0 0 0
9 8 7 6
0 0
BOFF
SMP
REC
0 0 0 0
Description
f sys/2 or EXTAL
----------------------------------------- -
=
PRESDIV + 1
= (PSEG1 + 1) time quanta
= (PSEG2 + 1) time quanta
Access: User read/write
21 20 19 18
PSEG1
0 0 0 0
5 4 3 2
TSYN LBUF LOM
0 0 0 0
FlexCAN
17 16
PSEG2
0 0
1 0
PROPSEG
0 0
Eqn. 23-1
Eqn. 23-2
Eqn. 23-3
Eqn. 23-4
23-9